PDCD1 and carcinoma of esophagus: Studies in oesophageal cancer have shown that high expression of PD-1/PDL-1 within the tumour microenvironment, in addition to lower CD8 lymphocyte infiltration, correlates with poorer prognosis in both squamous and adenocarcinoma [38,39], although this association has not been confirmed in all studies [40,41].